The research objective of this Faculty Early Career Development (CAREER) project is to develop a unified, scalable approach for soil liquefaction deformation analysis from micro to macro-scale. Earthquakes are among the most deadly and expensive natural disasters affecting our society. One of the leading causes of loss during earthquakes is seismically-induced displacements due to seismic compression (i.e. accrual of contractive volumetric strains in unsaturated soils during earthquake shaking), ground softening or soil liquefaction. The majority of research in soil liquefaction engineering has focused on the assessment of the likelihood of "triggering" of liquefaction, however much remains to be done with regards to the assessment of liquefaction-induced deformations. Yet, to engineer effective and efficient liquefaction hazard mitigation techniques, a thorough understanding of the development of liquefaction and its consequences is needed. This CAREER award presents a next-generation integration of 3D Discrete Element Modeling (DEM) and unique large-scale experiments for understanding post-liquefaction stability and ground deformation. The overarching research goal is to identify and quantify the physical and environmental parameters that affect the cyclic response of granular soils at the micro- and meso-scale particularly and relate them to the macro-scale (i.e. field) response and deformations. Soil exhibits a highly complex response to applied loads and deformations due to its particulate nature. It is widely recognized that especially during cyclic loading, it is this particulate nature of the soil and the particle morphology (i.e. particle aspect ratio and angularity) that mostly affects its response and its associated deformations. This research will (a) characterize particle morphology of granular assemblies and investigate the cyclic response of dry and saturated granular soils at the micro- and meso-scale by combining CSS laboratory tests and 3D DEM analyses, (b) study the micromechanical aspects of soil fabric changes and void ratio redistribution during cyclic loading using 3D DEM analysis and (c) develop a framework for scaling the micro (i.e. particle-to-particle contact) and meso-scale (i.e. particle assembly) behavior of granular soils to the macro-scale (i.e. field) response by simulating select centrifuge experiments reported in the literature and one proof-of-concept case-history, and investigating the input model parameters that control the transition to the macro-scale response. Recent advances in parallel computing will be employed to reduce computational effort of the 3D DEM. A custom-made TST (Translucent Segregation Table) and 12" CSS (Cyclic Simple Shear) laboratory device will be employed to characterize for the first time the particle morphology of thousands of particles that will then be cyclically sheared. The large-scale CSS apparatus can accommodate gravel-size particle specimens of known total number of particles and particle morphology allowing for a particle-to-particle simulation using the 3D DEM. Such a 1:1 approach of experimentation and DEM simulations is attempted for the first time using real soils.
This project's approach has the potential to transform the field of soil liquefaction engineering by providing more reliable estimates of liquefaction-induced deformations. A better understanding of the micro-scale response of granular soils under cyclic loading with respect to displacement can lead to a better evaluation of the performance of earthen structures during earthquake loads and also of the assessment of the effectiveness of mitigation measures for critical engineered structures such as earth or rockfill dams, levees, harbor frontages, bridge abutments, and pile and pier foundations. The educational plan of this study focuses on testing the hypothesis that providing an academic and research environment rich in real-life applications and socially relevant examples, will improve female undergraduate student retention in geotechnical engineering. To this effect, the PI intends to (a) introduce undergraduate female students to research projects by capitalizing on programs within UMich, (b) develop a series of in-class presentations, handout materials and questionnaires for the undergraduate course on geotechnical engineering to introduce real-world applications and positive social outcomes from civil engineering projects and (c) develop a new course on Computational Geomechanics.
